The present invention relates generally to telemetry systems for uplink and downlink telemetry transmission between an implantable medical device (IMD) and an external medical device (EMD) such as a programmer or monitor and more specifically to a method for ensuring that the telemetry link is between an intended, rather than an unintended, implantable medical device and the external medical device.
In the context of programming the operating modes or parameters of an IMD or in receiving information from an IMD, it is vital to ensure that programming commands not be received by an IMD other than the device intended to be programmed and that the source of any up-linked information from an IMD is properly identified. In most currently available systems, the programmer must be placed in close proximity to the implanted device, typically by means of a programming head in contact with the patient""s body. In such cases, there is little likelihood of confusion as to the identity of the implanted device with which the programmer is communicating.
More recently it has been proposed to provide communication systems for implantable devices in which the programming head is done away with, and communication occurs directly between the implanted medical device and a programmer or monitor which, may be located some distance from the patient. Such systems are disclosed in U.S. Pat. No. 5,404,877 issued to Nolan et al, and U.S. Pat. No. 5,113,869 issued to Nappholz. In the Nappholz patent, in particular, broadcasting RF signals from an implanted device to a programmer or monitor that may be located some feet away from the patient is suggested. Such a communication system is also disclosed in U.S. patent application No. 09/303,178 for a xe2x80x9cTelemetry System For Implantable Medical Devicesxe2x80x9d, filed Apr. 30, 1999 by Villaseca et al., which application is incorporated herein by reference in its entirety. In use of such systems, it is possible that multiple patients, each with an implanted device, may simultaneously be within communication range of the associated external device. In such cases, even if a telemetry link is established between the external device and an implanted device, there may still be uncertainty as to which patient""s device is communicating with the external device.
In the context of a telemetry system for communications between an implanted medical device and an associated external medical device located at a distance from the implanted device, the present invention is intended to assure that there is no ambiguity as to which implanted device is communicating with the external device or as to which patient has the device implanted. The invention accomplishes this result by providing a mechanism for indicating which of a number of devices within the communication range of the external device is implanted in a specific patient.
The external device preferably issues a request for communication, which may be received by any of a population of implantable devices that employ the inventive telemetry system. Those devices within range of the external device may in response send a telemetry transmission indicating that the request for communication has been received. This transmission preferably includes an identifier unique to the implanted device. A separate mechanism is provided for activating only the implantable device within a specific patient to send a telemetry transmission including an event signal indicative that the implanted device has been so activated. For example, per the direction of the physician or other individual operating the external device, a magnet may be placed adjacent the device implanted in a specified patient, triggering the uplink transmission of an event signal responsive to the magnet placement. The event signal may also include an identifier unique to the implanted device. The identifier may be used to subsequently communicate only with the device implanted in the specified patient.
If no event signal is received, the device implanted in the specified patient is understood to be either incompatible with the inventive telemetry system or out of range. If the external device receives an up-linked event signal, it is displayed to the operator or triggers a signal indicating its receipt. The operator may then determine whether the received event signal correlates in time to the response-provoking event. If so, the operator can conclude that the device that transmitted the event signal is the device with which communication is desired, and may initiate a telemetry session with that implanted, device. Alternatively, the external device may initiate a telemetry session with an implanted device prior to receipt of an uplink signal from the device, and may use the later uplinked event signal to confirm that communication is underway with the desired implanted device. In such embodiments, receipt of the uplinked event signal may serve as a prerequisite for continuation of the telemetry session and reprogramming of the implanted device.
Other mechanisms for triggering the transmission of the event signal may include, for example, application of pressure to a patient""s body, for example by physical impact such as by tapping adjacent the implanted device; audio activation by means of a tone generator, electrical activation by means of an electrical signal applied to the patient""s body or activation using an RF signal applied by means other than the remotely located external device.